In many implementations, inspected objects are imaged and are searched thereafter to discover target patterns. For example, aerial images may be searched for enemy tanks, textile fabric imaged during manufacture may be searched for holes, and electronic circuits, such as wafers, may be imaged and searched for defects.
Taking the case of defects searched during manufacture of wafers as an example, it is clear that while defects can damage the proper operability of the electronic circuit, impact of different defects on the operation of the electronic circuit may vary. Therefore, some defects may be of no substantial interest to the inspecting party, e.g. if their impact on circuit operation is low. Furthermore, knowledge regarding the different defects may be useful for manufacturing of future similar electronic circuits.
FIGS. 1A and 1B illustrate two types of defects in an electronic circuit, wherein each of FIGS. 1A and 1B illustrates an electronic circuit (such as a wafer), scanned using electron beam inspection. The grey level in each one of the circuits illustrated in FIGS. 1A and 1B is indicative of the pattern of the electronic circuit in that part of the wafer. For example, materials of different conductivity (such as a conducting material and an isolating material) may have different reflection indexes which may be translated to different grey levels. The following discussion pertains to an example in which substantially different grey level values in the image are indicative of different materials of substantially different electrical conductivity.
Defects 10a and 10c (also denoted “edge roughness” defects) are located on the boundary of an area of the imaged layer of the wafer between two different materials. Therefore, the electronic effect of such a defect is relatively limited, and under some circumstances such a defect may be of little interest.
Defects 10b and 10d, on the other hand (also denoted “short gate” defects), are located between two areas of the imaged layer of similar materials, and may indicate a conductive connection between two parts of the electronic circuits which ought to be isolated from each other. Since the electronic effects of such a defect may be relatively significant, under some circumstances such a defect may be further inspected—e.g. in a higher inspection resolution and/or using slower and more in-depth image analysis.